A comparative study of work function variations in III-V heterojunction and homojunction tunnel field-effect transistors

In this paper, we present a comparative study on the impact of work function variations (WFV) between the III-V heterojunction and homojunction tunnel field-effect transistors (TFETs) vis TCAD simulation. It reveals that, in general, the current variation of both devices decrease as the gate voltage increases, and the threshold voltage variations generally increase with the increase of threshold current. However, in comparison to homojunction TFET, heterojunction TFET exhibits the following two differences. 1) The current fluctuation is stronger near the device's OFF-state and weaker near the ON-state, and thus it has a stronger dependence on bias. 2) Both the threshold voltage fluctuations and its dependence on the threshold current are weaker. On the other hand, with an increase in grain size, both homojunction and heterojunction devices manifest more prominent performance fluctuations. Moreover, the dependence of these fluctuations on grain size is roughly comparable for these two device types. Finally, it is observed that 1) the significant current fluctuation at the OFF-state can be mitigated when the device's OFF-state is designed within a region with weaker gate control, and 2) the current normalized coefficient of variation parameter may be unreliable to assess the fluctuation for the case with a few “abnormal” high current values.